Relative radial velocities of HAT-P-4 and HAT-P-14

HAT-P-4b is prograde, with a sky-projected spin-orbit angle of {lambda}=-4.9+/-11.9{deg}. In contrast, HAT-P-14b is retrograde, with {lambda}=189.1+/-5.1{deg}.

These results conform with a previously noted pattern among the stellar hosts of close-in giant planets: hotter stars have a wide range of obliquities and cooler stars have low obliquities. This, in turn, suggests that three-body dynamics and tidal dissipation are responsible for the short-period orbits of many exoplanets. In addition, our data revealed a third body in the HAT-P-4 system, which could be a second planet or a companion star.